linux-kernel - Re: [PATCH 2/3] zram: do not use copy_page with non-page alinged address

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Message-ID: <20170414154015.GB16910@bgram>
Date:   Sat, 15 Apr 2017 00:40:15 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        kernel-team@....com, stable@...r.kernel.org
Subject: Re: [PATCH 2/3] zram: do not use copy_page with non-page alinged
 address

On Fri, Apr 14, 2017 at 02:41:05PM +0900, Sergey Senozhatsky wrote:
> Hello,
> 
> On (04/13/17 09:17), Minchan Kim wrote:
> > The copy_page is optimized memcpy for page-alinged address.
> > If it is used with non-page aligned address, it can corrupt memory which
> > means system corruption. With zram, it can happen with
> > 
> > 1. 64K architecture
> > 2. partial IO
> > 3. slub debug
> > 
> > Partial IO need to allocate a page and zram allocates it via kmalloc.
> > With slub debug, kmalloc(PAGE_SIZE) doesn't return page-size aligned
> > address. And finally, copy_page(mem, cmem) corrupts memory.
> 
> which would be the case for many other copy_page() calls in the kernel.
> right? if so - should the fix be in copy_page() then?

I thought about it but was not sure it's good idea by several reasons
(but don't want to discuss it in this thread).

Anyway, it's stable stuff so I don't want to make the patch bloat.
If you believe it is right direction and valuable, you could be
a volunteer. :)

Thanks.